AIM: To establish reference values for the nuchal translucency (NT) thickness in Japanese fetuses. MATERIAL AND METHODS: Ultrasonographic measurements of the crown-rump length (CRL) and NT were performed from 11 to 13 + 6 weeks of gestation in consecutive Japanese fetuses examined during prenatal visits between February 2011 and January 2012. The median, 5th and 95th percentiles of the NT thickness with 5 mm intervals of the CRL were confirmed. RESULTS: A total of 970 cases were enrolled in the study. The median NT thickness for a CRL between 45 and 80 mm ranged from 1.2 mm to 1.9 mm, and the 95th percentile of these values ranged from 2.1 mm to 3.2 mm, respectively. CONCLUSION: The reference values for the NT thickness in Japanese fetuses were determined. These values should be useful for fetal biometry, morphological assessment and first trimester screening for chromosomal abnormalities in Japan.